NASA Technical Reports Server (NTRS) 20110005475: Alpha voltaic batteries and methods thereof

0.76 MB·English

by  NASA Technical Reports Server (NTRS)

United States Patent
(12) (lo) Patent No.: US 7,867,640 B2
Raffaelle et al. (45) Date of Patent: Jan. 11, 2011
(54) ALPHA VOLTAIC BATTERIES AND (58) Field of Classification Search ..................... 429/5;
METHODSTHEREOF 136/202; 310/301, 303, 305
See application file for complete search history.
(75) Inventors: Ryne P. Raffaelle, Honeoye Falls, NY
(56) References Cited
(US); Phillip Jenkins, Cleveland
Heights, OH (US); David Wilt, Bay U.S. PATENT DOCUMENTS
Village, OH (US); David Scheiman, 3,994,718 A * 11/1976 Berndt et al . .................. 420/1
Cleveland, OH (US); Donald Chubb, 5,082,505 A * 1/1992 Cota et al . .................. 136/253
Olmsted Falls, OH (US); Stephanie 5,859,484 A * 1/1999 Mannik et al . .............. 310/303
Castro, Westlake, OH (US) 6,479,743 B2 * 11/2002 Vaz ............................ 136/253
OTHER PUBLICATIONS
(73) Assignees: Rochester Institute of Technology,
Pfann et al., "Radioactive and Photoelectric p-n Junction Power
Rochester, NY (US); The United States Sources," Journal of Applied Physics 25(11):1422-1434 (1954).
of America as represented by the Rybicki, G., "Silicon Carbide Alphavoltaic Battery," Proceedings of
Administrator of the National the 25th IEEE Photovoltaic Specialists Conference, Washington,
Aeronautics and Space D.C., pp. 93-96 (1996).
Gailey et al, "Photovoltaic Development For Alpha Voltaic Batter-
Administration, Washington, DC (US)
ies," NASA Glenn Research Center, pp. 106-109 (2005) (http://
ieexplore.ieee.org/iel5/9 8 89/3 142 6/0 14 8 8 0 8 0.
(*) Notice: Subject to any disclaimer, the term of this
pdVarnumbei-1488080).
patent is extended or adjusted under 35
* cited by examiner
U.S.C. 154(b) by 0 days.
Primary Examiner Dah-Wei D Yuan
(21) Appl. No.: 12/196,790 Assistant Examiner Maria J Laios
(74) Attorney, Agent, or Firm Nixon Peabody LLP
(22) Filed: Aug. 22, 2008
(57) ABSTRACT
(65) Prior Publication Data
An alpha voltaic battery includes at least one layer of a semi-
US 2008/0318357 Al Dec. 25, 2008 conductor material comprising at least one p/n junction, at
least one absorption and conversion layer on the at least one
Related U.S. Application Data layer of semiconductor layer, and at least one alpha particle
emitter. The absorption and conversion layer prevents at least
(62) Division of application No. 11/093,134, filed on Mar.
a portion of alpha particles from the alpha particle emitter
29, 2005.
from damaging the p/n junction in the layer of semiconductor
(60) Provisional application No. 60/557,993, filed on Mar. material. The absorption and conversion layer also converts at
31, 2004. least a portion of energy from the alpha particles into elec-
tron-hole pairs for collection by the one p/n junction in the
(51) Int. Cl. layer of semiconductor material.
H01M14100 (2006.01)
(52) U.S. Cl . .......................................................... 429/5 23 Claims, 4 Drawing Sheets
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SCHEMATIC OF AN ALPHA VOLTAIC BATTERY
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US 7,867,640 B2
1 2
ALPHA VOLTAIC BATTERIES AND A method for generating power in accordance with
METHODSTHEREOF embodiments of the present invention includes emitting alpha
particles from an alpha particle emitter into at least one
This application is a divisional of prior application Ser. No. absorption and conversion area. At least a portion of the
11/093,134, filed Mar. 29, 2005, which claims the benefit of 5 emitted alpha particles from the alpha particle emitter are
U.S. Provisional Patent Application Ser. No. 60/557,993 filed prevented from damaging the p/n junction in the layer of
Mar. 31, 2004, which are hereby incorporated by reference in semiconductor material with the absorption and conversion
their entirety. layer. At least a portion of energy from the alpha particles is
The subject matter of this application was made with sup- converted into electron-hole pairs for collection by the p/n
port from the United States Government under NASA Grant io junction in the layer of semiconductor material.
No. NAG3-2595. The United States Government has certain The present invention provides alpha voltaic batteries
rights. whose performance does not degrade in a matter of hours
because of damage to the layer of semiconductor material
FIELD OF THE INVENTION from the emitted alpha particles. The present invention also
15 provides power supplies which are both small and have a long
The present invention generally relates to batteries and, life span and thus are suitable for a variety of technologies,
more particularly, alpha voltaic batteries and methods including micro electrical mechanical systems (MEMS). Fur-
thereof. ther, the alpha voltaic batteries in accordance with the present
invention can be scaled to higher power levels which make
BACKGROUND 20 them useful in another wide range of technologies, such as a
power source of deep space missions.
The concept of an alpha voltaic battery was proposed in
1954 as disclosed in W. G. Pfann and W. van Roosbroeck, BRIEF DESCRIPTION OF THE DRAWINGS
Journal of Applied Physics, Volume 25, No. 11, pp. 1422-
1434, November 1954, which is herein incorporated by ref-
25 FIG.1 is apartial side, cross sectional and partial schematic
erence. In an alpha voltaic battery a radioactive substance that diagram of an alpha voltaic battery in accordance with
emits energetic alpha particles is coupled to a semiconductor embodiments of the present invention;
p/n junction diode. As the alpha particles penetrate into the
FIG. 2 is apartial side, cross sectional and partial schematic
p/n junction, they decelerate and give up their energy as
diagram of a bi-facial alpha voltaic battery in accordance with
electron-hole pairs. These electron-hole pairs are collected by 30 other embodiments of the present invention;
the p/n junction and converted into useful electricity much
FIGS. 3A-3D are side, cross sectional views of alpha vol-
like a solar cell.
taic battery in accordance with embodiments of the present
The main reason alpha voltaic batteries are not commer-
invention; and
cially successful is that the alpha particles damage the semi-
conductor material so as to degrade its electrical performance 35 FIG. 4 is a graph of Nano Amps v. Volts for a prototype of
an alpha voltaic battery operating at temperatures down to
in just a matter of hours as disclosed in G. C. Rybicki, C. V.
Aburto, R. Uribe, Proceedings of the 25th IEEE Photovoltaic about —135° C.
Specialists Conference, pp. 93-96, 1996, which is herein
incorporated by reference. DETAILED DESCRIPTION
40
SUMMARY Alpha voltaic batteries 10(1) and 10(6) in accordance with
embodiments of the present invention are illustrated in FIGS.
An alpha voltaic battery in accordance with embodiments 1-31). The batteries 10(1)-10(6) each include an intermediate
of the present invention includes at least one layer of a semi- or absorption and conversion layer 12(1)-12(6) with an alpha
conductor material comprising at least one p/n junction, at 45 particle emitter or source 14(1)-14(6) and one or more layers
least one absorption and conversion layer on the at least one of semiconductor material 18(1)-18(6) and 22(1)-22(3),
layer of semiconductor layer, and at least one alpha particle although the batteries 10(1)-10(6) can each comprise other
emitter. The absorption and conversion layer prevents at least numbers and types of elements in other configurations. The
a portion of alpha particles from the alpha particle emitter present invention provides alpha voltaic batteries whose per-
from damaging the p/n junction in the layer of semiconductor 50 formance does not degrade in a matter of hours because of
material. The absorption and conversion layer also converts at damage to the layer semiconductor material from the alpha
least a portion of energy from the alpha particles into elec- particles.
tron-hole pairs for collection by the one p/n junction in the Referring more specifically to FIG. 1, an alpha voltaic
layer of semiconductor material. battery 10(1) in accordance with embodiments of the present
A method for making an alpha voltaic battery in accor- 55 invention is illustrated. The alpha particle emitter 14(1) emits
dance with embodiments of the present invention includes energetic alpha particles which are converted by the alpha
providing at least one layer of a semiconductor material com- voltaic battery 10(1) into energy. The alpha particle emitter
prising at least one p/n junction, putting at least one absorp- 14(1) is embedded in a metal foil 16, although the alpha
tion and conversion layer on the at least one layer of semi- particle emitter 14(1) could be embedded or connected to
conductor layer, and providing at least one alpha particle 60 other types and numbers of layers of material or materials in
emitter. The absorption and conversion layer prevents at least other configurations, such as in the absorption and conversion
a portion of alpha particles from the alpha particle emitter layer 12(2) as shown and described with reference to FIG. 2.
from damaging the p/n junction in the layer of semiconductor Referring back to FIG. 1, in these embodiments the alpha
material. The absorption and conversion layer also converts at particle emitter 14(1) comprises Am-241 which is thermally
least a portion of energy from the alpha particles into elec- 65 diffused in the metal foil 16 and is then over-coated with
tron-holepairs for collection by the p/n junction in the layer of another metal, such as silver, to form the metal foil 16 with the
semiconductor material. embedded alpha particle emitter 14(1), although other types
US 7,867,640 B2
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of alpha particle emitters which are embedded or configured less near the layer of semiconductor material 18(4) helps to
in other manners could be used. make an effective battery 10(4) while minimizing any pos-
The intermediate or absorption and conversion layer 12(1) sible radiation to the layer of semiconductor material 18(4).
is deposited on the metal foil 16 with the embedded alpha Similarly, referring to FIG. 3C, the alpha particle emitter
particle emitter 14(1), although other types and numbers of 5 14(5), which for illustration purposes only is illustrated as
absorption and conversion layers in other configurations dots, is distributed in a graded fashion throughout the absorp-
could be used. The absorption and conversion layer 12(1) tion and conversion layer 12(5) with proportionally less alpha
prevents alpha particles from the alpha particle emitter 14(1) emitting material as the absorption and conversion layer
from damaging one or more p/n junctions in the layer of 12(5) nears each of the layers of semiconductor material
semiconductor material 18(1). The absorption and conver- io 18(5) and 22(2) with the p/n junction. Referring to FIG. 3D,
sion layer 12(1) also successfully converts the photons or the alpha particle emitter 14(6) and the absorption and con-
energy from the alpha particles into electron-hole pairs for version layer 12(6) are in a multilayered film arrangement
collection by the p/n junction in the layer of semiconductor between the layers of semiconductor material 18(6) and
material 18(1). The thickness of the absorption and conver- 22(3), although other numbers of layers of alpha particle
sion layer 12(1) depends upon the energy or the alpha par- 15 emitters, absorption and conversion layers, and/or layers of
ticles and the resulting penetration depth in the absorption semiconductor material could be used.
and conversion layer 12(1). The thickness of the absorption Referring back to FIG. 1, an interface 19 between the base
and conversion layer 12(1) can be chosen to prevent any layer 16 with the alpha particle emitter 14(1) and the absorp-
radiation damage to the layer of semiconductor material tion and conversion layer 12(1) is substantially reflective of
18(1) or to permit partial amounts of the energy to be depos- 20 the photons emitted by the absorption and conversion layer
ited into the layer of semiconductor material 18(1) and to 14(1). With this reflection at the interface 19, the photons
decrease the self-absorption of photons by absorption and emitted by the absorption and conversion layer 14(1) towards
conversion layer 12(1). For example, a thickness of the the base layer 16 are be reflected to the p/n junction in the
absorption and conversion layer 12(1) can be determined and layer of semiconductor material 18(1) for collection. The
selected to achieve a desired minimum lifespan for the battery 25 natural reflectivity of alpha particle emitter 14(1) will cause
10(1)-10(6) and power output by providing a sufficient thick- reflection, although other ways of achieving the desired
ness to protect the layer of semiconductor material 18(1) reflectivity can be used, such as an optional thin metal coating
while permitting a sufficient amount of the photons to reach 21 on the metal foil 16 at the interface 19, although other
the layer of semiconductor material 18(1) for conversion to numbers and types of at least partially reflective coatings at
power. 30 other locations can be used. By way of example only, the
In these embodiments the absorption and conversion layer coating 21 could be the normal gold coating applied to seal
12(1) comprises a layer of phosphor, such as ZnS:Ag, which most solid sample sources. The reflectivity of the surface of
fluoresces photons of approximately 2.66 eV (465 mn wave- the metal foil 16 is directly related to the thickness of the
length) in energy, although other types and numbers of metal foil 16, but the thickness will be inversely proportional
absorption and conversions layers could be used. By way of 35 to the amount of alpha energy which it passes.
example only, other materials which could be used for the The layer of semiconductor material 18(1) is deposited on
absorption and conversion layer 12(1) include rare earth a surface of the absorption and conversion layer 12(1),
oxides or rare earth doped garnet crystals and nano scale mate- although other types and numbers of layers of semiconductor
rials known as "quantum dots" that exhibit flourescence material in other configurations could be used. In these
under particle radiation, although other types of materials 40 embodiments, the layer of semiconductor material 18(1) with
could be used. Materials that fluoresce under particle radia- the p/n junction is a high bandgap "solar cell', although other
tion, collectively known as phosphors, can convert particle numbers of p/n junctions could be used. By way of example
radiation into photons with very high efficiency. only, the types of layers of semiconductor materials which
The alpha particle emitter 14(1) is placed adjacent the could be used include, by way of example only, GaAs, GaInP,
absorption and conversion layer 12(1) and is embedded in the 45 SiC, Si, or other III-V, II-VI or group IV semiconductors. The
metal foil 16 as shown in FIG. 1, although other numbers and layer of semiconductor material 18(1) has a high bandgap
types of elements in other arrangements can be used. By way ranging between about 1 eV and about 3 eV, although the high
of example only, other arrangements for alpha particle emit- bandgap for the layer of semiconductor material 18(1) could
ters 14(3)-14(6) are illustrated in alpha voltaic batteries have other ranges.
10(3)-10(6) shown in FIGS. 3A-3D. Alpha voltaic batteries 50 The operation of the alpha voltaic battery 10(1) will now be
10(3)-10(6) have a like structure and operation as the corre- described with reference to FIG. 1. Alpha particles emitted
sponding alpha voltaic batteries 10(1) and 10(2), except as from the alpha particle emitter 14(1) embedded in the metal
described herein. Additionally, elements in FIGS. 3A-3D foil 16 are emitted into the absorption and conversion layer
which are like those in FIGS. 1 and 2 have like reference 12(1). The alpha particles decelerate in the absorption and
numerals. 55 conversion layer 12(1) creating electron-hole pairs. Instead of
Referring to FIG. 3A, the alpha particle emitter 14(3), being collected by a p/n junction in the layer of semiconduc-
which for illustration purposes only is illustrated as dots, is tor material 18(1), the electron-hole pairs in the absorption
distributed homogeneously throughout the absorption and and conversion layer 12(1) simply recombine and emit pho-
conversion layer 12(3) which is adjacent the layer of semi- tons.
conductor material 18(3) with a p/n junction. Referring to 60 The emitted photons in the absorption and conversion layer
FIG. 313, the alpha particle emitter 14(4), which for illustra- 12(1) are either emitted towards the layer of semiconductor
tion purposes only is illustrated as dots, is distributed in a material 12(1) or are substantially reflected at the interface
graded fashion throughout the absorption and conversion between the metal foil 16 and the absorption and conversion
layer 12(4) with proportionally less alpha emitting material as layer 12(1) towards the layer of semiconductor material
the absorption and conversion layer 12(4) nears the layer of 65 12(1). Since the photons have energy greater than the band-
semiconductor material 18(4) with the p/n junction. Distrib- gap of the p/n junction in the layer of semiconductor material
uting the alpha particle emitter 14(4) in a graded fashion with 18(1), the photons are absorbed in the p/n junction layer of
US 7,867,640 B2

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semiconductor material 12(1) creating electron-hole pairs layers of semiconductor materials 18(2) and 22(1), while

that are converted into useful electricity. This generated elec- minimizing any damage to the layers of semiconductor mate-

tricity or power is transferred to a load 20(1) which is coupled rials 18(2) and 22(1) and to the absorption and conversion

between the absorption and conversion layer 12(1) and the layer 12(2).
layer of semiconductor material 18(1) across the p/njunction. 5 In these embodiments the absorption and conversion layer

Accordingly, with the absorption and conversion layer 12(1), 12(2) comprises a layer of phosphor, such as ZnS:Ag, which

the p/n junction in the layer of semiconductor material 18(1) fluoresces photons of approximately 2.66 eV (465 mu wave-

is protected from the harmful effects of the alpha particles length) in energy, although other types and numbers of

from the alpha emitter 14(1), but still recovers the energy absorption and conversions layers could be used. By way of
from the alpha radiation which is converted to useful power. io example only, other materials which could be used for the

Referring to FIG. 2, a schematic diagram of a bi-facial absorption and conversion layer 12(2) include rare earth

alpha voltaic battery 10(2) in accordance with other embodi- oxides or rare earth doped garnet crystals and nano scale mate-

ments of the present invention is illustrated. The alpha par- rials known as "quantum dots" that exhibit fluorescence

ticle emitter 14(2) emits energetic alpha particles which are under particle radiation, although other types of materials
converted by the alpha voltaic battery 10(2) into energy. The 15 could be used. Materials that fluoresce under particle radia-
alpha particle emitter 14(2) is embedded in an absorption and tion, collectively known as phosphors, can convert particle

conversion layer 12(2), although the alpha particle emitter radiation into photons with very high efficiency.

14(2) could be embedded or connected to other types and The layers of semiconductor material 18(2) and 22(1) are

numbers of layers of material or materials in other configu- deposited on opposing surfaces of the absorption and conver-
rations. For example, the alpha particle emitter 14(2) could be 20 sion layer 12(2), although other types and numbers of layers

in a multilayered film between the layers of semiconductor of semiconductor material in other configurations could be

material 18(2) and 22(1) comprising with alternating layers used. In these embodiments, each of the layers of semicon-

of the alpha particle emitter and the absorption and conver- ductor material 18(2) and 22(1) have a p/n junction and com-

sion layer. In another embodiment, the alpha particle emitter prise a high bandgap "solar cell', although other numbers of
14(2) could be distributed homogeneously throughout the 25 p/n junctions could be used in each of the layers of semicon-

absorption and conversion layer 12(2). In yet another embodi- ductor material 18(2) and 22(1). By way of example only, the

ment, the alpha particle emitter 14(2) could be distributed in types of layers of semiconductor materials which could be

a graded fashion throughout the absorption and conversion used include, by way of example only, GaAs, GaInP, SiC, Si,

layer 12(2) with proportionally less alpha emitting material as or other III-V, II-VI or group IV semiconductors. Each of the
the absorption and conversion layer 12(1) nears each of the 30 layers of semiconductor material 18(2) and 22(1) has a high

layers of semiconductor material 18(2) and 22(1). Distribut- bandgap ranging between about I eV and about 3 eV,

ing the alpha particle emitter 14(2) in a graded fashion with although the high bandgap for each of the layers of semicon-

less near each of the layers of semiconductor material 18(2) ductor material 18(2) and 22(1) could have other ranges.

and 22(l) helps to make an effective battery while minimizing The operation of the alpha voltaic battery 10(2) will now be
any possible radiation to each of the layers of semiconductor 35 described with reference to FIG. 2. Alpha particles emitted

material 18(2) and 22(1). In these embodiments the alpha from the alpha particle emitter 14(2) embedded in the absorp-

particle emitter 14(2) comprises Am-241 which is thermally tion and conversion layer 12(2) are emitted into the absorp-

diffused in the absorption and conversion layer 12(2), tion and conversion layer 12(2). The alpha particles deceler-

although other types of alpha particle emitters which are ate in the absorption and conversion layer 12(2) creating
embedded or configured in other manners could be used. 40 electron-hole pairs. Instead of being collected by the p/n

The absorption and conversion layer 12(2) comprises a junction in each of the layers of semiconductor material 18(2)

single layer between layers of semiconductor material 18(2) and 22(1), the electron-hole pairs in the absorption and con-

and 22(1), although other types and numbers of absorption version layer 12(2) simply recombine and emit photons.

and conversion layers in other configurations could be used. The emitted photons in the absorption and conversion layer
The absorption and conversion layer 12(2) prevents alpha 45 12(2) are either emitted towards the layer of semiconductor

particles from the alpha particle emitter 14(2) from damaging material 18(2) or towards the layer of semiconductor material

one or more p/n junctions in the layers of semiconductor 22(1). Since the photons have energy greater than the band

material 18(2) and 22(1). The absorption and conversion gap of the p/n junction in each of the layers of semiconductor

layer 12(2) also successfully converts the photons or energy material 18(2) and 22(1), the photons are absorbed in the p/n
from the alpha particles into electron-hole pairs for collection 50 junction in each of the layers of semiconductor material 18(2)

by the p/n junction in each of the layers of semiconductor and 22(1) creating electron-hole pairs that are converted into

material 18(2) and 22(1). The absorption and conversion useful electricity. This generated electricity or power is trans-

layer 12(2) comprises a single layer of phosphor, although ferred to loads 20(2) and 20(3). Load 20(2) is coupled across

again like the absorption and conversion layer 14(1), the the p/n junction of the layer of semiconductor material 18(2)
absorption and conversion layer 12(2) can have other types 55 and load 20(3) is coupled across the p/n junction of the layer

and numbers of layers in other configurations, such as a of semiconductor material 22(1). Accordingly, with the

multilayer design alternating with layers of the alpha particle absorption and conversion layer 12(2), the p/n junction in

emitter between or a composite of the alpha particle emitter each of the layers of semiconductor material 18(2) and 22(1)

and the absorption and conversion layer in which the alpha is protected from the harmful effects of the alpha particles
particle emitter is homogeneously or graded throughout the 60 from the alpha emitter 14(2), but still recovers the energy

absorption and conversion layer 12(2). The number of layers from the alpha radiation.

and/or composition and material distribution depends on the The emerging technologies of micro electrical mechanical

particular material used for absorption and conversion layer systems (MEMS) are a perfect application for alpha voltaic

12(2) and the particular alpha source material utilized for the batteries in accordance with the present invention. The
alpha particle emitter 14(2). The absorption and conversion 65 present invention provides a long life power source that sim-

layer 12(2) and the alpha particle emitter 14(2) are combined ply did not exist for these devices prior to this invention.

to provide the maximum photon output to the surrounding Additionally, the present invention is very suitable for inte-
US 7,867,640 B2
7 8
grating batteries directly on the semiconductor for a "battery- 5.The method as set forth in claim 1 further comprising
on-a-chip" concept. Alpha voltaic batteries in accordance embedding the at least one alpha particle emitter in at least a
with the present invention could produce power on the order portion of the at least one absorption and conversion layer.
of micro-Watts, sufficient for many MEMS applications.
6.The method as set forth in claim 5 wherein the at least
With the present invention, scaling to higher power levels 5 one alpha particle emitter is substantially homogeneously
suitable for deep space missions (100's of Watts) is also
disbursed through the at least one absorption and conversion
possible. Alpha voltaic batteries in accordance with the
layer.
present invention have at least two unique properties when
compared to conventional chemical batteries that make them 7.The method as set forth in claim 5 wherein the at least
outstanding candidates for deep space missions: 1) The alpha io one alpha particle emitter is disbursed through the at least one
emitting materials have half-lives from months to 100's of absorption and conversion layer in a graded manner with
years, so there is the potential for "everlasting" batteries; and proportionally less of the at least one alpha particle emitter
2) Alpha voltaic batteries in accordance with the present near the at least one layer of semiconductor material.
invention can operate over a tremendous temperature range.
8.The method as set forth in claim 1 wherein the at least
Ordinary chemical batteries all fail at temperatures below 15 one alpha particle and the at least one absorption and conver-
—40° C., while alpha voltaic batteries in accordance with the
sion layer comprise a plurality of alternating layers.
present invention have been demonstrated to work at —135° C.
9.The method as set forth in claim 1 wherein the at least
as illustrated in the current (I)-voltage (V) graph in FIG. 4 for
a prototype of an alpha voltaic battery. one layer of semiconductor material has a high bandgap rang-
Having thus described the basic concept of the invention, it 20 ing between about 1 eV and about 3 eV.
will be rather apparent to those skilled in the art that the 10.The method as set forth in claim 1 further comprising
foregoing detailed disclosure is intended to be presented by putting at least one other layer of a semiconductor material
way of example only, and is not limiting. Various alterations, with at least one p/n junction on another surface of the at least
improvements, and modifications will occur and are intended one absorption and conversion layer.
to those skilled in the art, though not expressly stated herein.
25 11. A method for making an alpha voltaic battery, the
These alterations, improvements, and modifications are
method comprising:
intended to be suggested hereby, and are within the spirit and
scope of the invention. Additionally, the recited order of pro- providing at least one layer of a semiconductor material
cessing elements or sequences, or the use of numbers, letters, comprising at least one p/n junction;
or other designations therefore, is not intended to limit the 30 putting at least one absorption and conversion layer on the
claimed processes to any order except as may be specified in at least one layer of semiconductor layer, wherein the
the claims. Accordingly, the invention is limited only by the absorption and conversion layer comprises one of a rare
following claims and equivalents thereto. earth oxide, a rare earth doped garnet crystal, and quan-
tum dots; and
What is claimed is: 35 providing at least one alpha particle emitter, wherein the at
1. A method for making an alpha voltaic battery, the least one absorption and conversion layer prevents at
method comprising: least a portion of alpha particles from the at least one
providing at least one layer of a semiconductor material alpha particle emitter from damaging the at least one p/n
comprising at least one p/n junction; junction in the at least one layer of semiconductor mate-
putting at least one absorption and conversion layer on the 40 rial and converts at least a portion of energy from the
at least one layer of semiconductor material, wherein the alpha particles into electron-hole pairs for collection by
absorption and conversion layer comprises at least one
the at least one p/n junction in the at least one layer of
layer of a fluorescent material; and
semiconductor material.
providing at least one alpha particle emitter, wherein the at
45 12. A method for making an alpha voltaic battery, the
least one absorption and conversion layer prevents at
method comprising:
least a portion of alpha particles from the at least one
alpha particle emitter from damaging the at least one p/n providing at least one layer of a semiconductor material
junction in the at least one layer of semiconductor mate- comprising at least one p/n junction;
rial and converts at least a portion of energy from the putting at least one absorption and conversion layer on the
50
alpha particles into electron-hole pairs for collection by at least one layer of semiconductor layer; and
the at least one p/n junction in the at least one layer of
providing at least one alpha particle emitter, wherein the at
semiconductor material.
least one absorption and conversion layer prevents at
2.The method as set forth in claim 1 further comprising
least a portion of alpha particles from the at least one
embedding the at least one alpha particle emitter in at least
55 alpha particle emitter from damaging the at least one p/n
one base layer, wherein the at least one absorption and con-
junction in the at least one layer of semiconductor mate-
version layer is on the at least one base layer and between the
rial and fluoresces photons in response to at least a
at least one base layer with the alpha particle emitter and the
portion of energy from the alpha particles for collection
at least one layer of a semiconductor material.
by the at least one p/n junction in the at least one layer of
3.The method as set forth in claim 2 wherein an interface
60 semiconductor material.
between the at least one absorption and conversion layer and
the at least one base layer to the at least one p/n junction in the 13. The method as set forth in claim 12 further comprising
at least one layer of semiconductor material is at least par- embedding the at least one alpha particle emitter in at least
tially reflective. one base layer, wherein the at least one absorption and con-
4.The method as set forth in claim 3 further comprising 65 version layer is on the at least one base layer and between the
providing at least one coating at the interface which provides at least one base layer with the alpha particle emitter and the
the at least partial reflectivity. at least one layer of a semiconductor material.
US 7,867,640 B2
9 10
14.The method as set forth in claim 13 wherein an interface proportionally less of the at least one alpha particle emitter
between the at least one absorption and conversion layer and near the at least one layer of semiconductor material.
the at least one base layer to the at least one p/n junction in the 19.The method as set forth in claim 12 wherein the at least
at least one layer of semiconductor material is at least par- one alpha particle and the at least one absorption and conver-
tially reflective. 5 sion layer comprise a plurality of alternating layers.
20.The method as set forth in claim 12 wherein the absorp-
15.The method as set forth in claim 14 further comprising
tion and conversion layer comprises at least one layer of a
providing at least one coating at the interface which provides
fluorescent material.
the at least partial reflectivity.
21.The method as set forth in claim 12 wherein the absorp-
16.The method as set forth in claim 12 further comprising io tion and conversion layer comprises one of a rare earth oxide,
embedding the at least one alpha particle emitter in at least a a rare earth doped garnet crystal, and quantum dots.
portion of the at least one absorption and conversion layer. 22.The method as set forth in claim 12 wherein the at least
17.The method as set forth in claim 16 wherein the at least one layer of semiconductor material has a high bandgap rang-
one alpha particle emitter is substantially homogeneously ing between about 1 eV and about 3 eV.
disbursed through the at least one absorption and conversion 15 23. The method as set forth in claim 12 further comprising
putting at least one other layer of a semiconductor material
layer.
with at least one p/n junction on another surface of the at least
18.The method as set forth in claim 16 wherein the at least
one absorption and conversion layer.
one alpha particle emitter is disbursed through the at least one
absorption and conversion layer in a graded manner with